remove the element attached to the image border

Question

I'm using OpenCV to detect Pneumonia in chest-x-ray using Image Processing, so I need to remove the attached area to the image border to get the lung only, can anyone help me code this in python?

This image explains what I want this image after applying this methods: resized, Histogram Equalization, otsu Thresholded and inverse binary Thresholded, morphological processes(opening then closing)

This is the Original Image Original Image

Answer 1

This is how I would approach the problem in Python/OpenCV. Add a white border all around, flood fill it with black to replace the white, then remove the extra border.

Input:

import cv2
import numpy as np

# read image
img = cv2.imread('lungs.jpg')
h, w = img.shape[:2]

# convert to gray
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

# add 1 pixel white border all around
pad = cv2.copyMakeBorder(gray, 1,1,1,1, cv2.BORDER_CONSTANT, value=255)
h, w = pad.shape

# create zeros mask 2 pixels larger in each dimension
mask = np.zeros([h + 2, w + 2], np.uint8)

# floodfill outer white border with black
img_floodfill = cv2.floodFill(pad, mask, (0,0), 0, (5), (0), flags=8)[1]

# remove border
img_floodfill = img_floodfill[1:h-1, 1:w-1]    

# save cropped image
cv2.imwrite('lungs_floodfilled.png',img_floodfill)

# show the images
cv2.imshow("img_floodfill", img_floodfill)
cv2.waitKey(0)
cv2.destroyAllWindows()